Caustic Soda Testing Methods | Sodium Hydroxide Testing Procedure

Determination of alkaline content by titration procedure or caustic soda (Sodium hydroxide) purity analysis procedure and purity of NaOH ( sodium hydroxide) pellets. 


a. 250ml conical flask.

b. Burette

c. 25ml volumetric pipette

d. 250ml volumetric flask


a. Standard 0.1(N) HCl solution

b. Phenolphthalein indicator

c. Methyl orange indicator


Accurately weigh out approx. 1.5195 gms. of caustic soda sample in a 250 ml. volumetric flask. Make up to the mark with distilled water and shake well to make a solution. 

Remove a 25ml portion of this solution in a 250ml conical flask and titrate with 0.1(N) HCl solution from a burette using a phenolphthalein indicator. Note the burette reading at this point.

Total alkalinity (%) = V1 (ml) X Normality HCl X 40

                                     ------------------------------------ = x%

                                       Wt. Of caustic sample

Now add Methyl Orange solution to this colorless solution in the conical flask. 

Continue titration till the orange color changes to red at the endpoint. Note the burette reading (V2 ).

Alkalinity as Na2CO3 (%) = V2 – V1 (ml) X Normality HCl X 5.3

--------------------------------------------- = y%

Wt. Of caustic sample

Assay of caustic soda = (x-y) %

Uses of caustic soda (sodium hydroxide)

Caustic soda, also known as sodium hydroxide (NaOH), is a versatile chemical compound with a wide range of uses in various industries.

1. Chemical Manufacturing:

Caustic soda is a fundamental ingredient in the production of various chemicals, including detergents, soaps, and cleaning agents. It's also used to create other chemicals like sodium salts, dyes, and pharmaceuticals.

2. Paper and Pulp Industry:

In the paper and pulp industry, caustic soda is used in the pulping process to break down lignin and separate fibers from wood. It's also used to bleach paper products and treat wastewater generated during production.

3. Textile Industry:

Caustic soda is used in the textile industry to remove natural fats, oils, and waxes from fabrics. This process, known as mercerization, enhances the appearance and properties of the textiles.

4. Aluminum Production:

In the aluminum industry, caustic soda is used to dissolve alumina (aluminum oxide) from bauxite ore during the production of aluminum. This process is called the Bayer process.

5. Petroleum Industry:

Caustic soda is used in refining petroleum products. It helps to remove impurities, such as sulfur compounds, from crude oil and improves the quality of the end products.

6. Food Processing:

In food processing, caustic soda is used for cleaning and sanitizing equipment and containers. It's also employed in processes like peeling fruits and vegetables and adjusting pH levels in food products.

7. Water Treatment:

Caustic soda is used in water treatment plants to adjust the pH levels of water. It can also be used for cleaning and disinfection purposes in water systems.

8. Cleaning Agents:

Household cleaning agents often contain caustic soda due to its ability to dissolve grease, oils, and other tough stains. However, caution is needed when using such products due to their corrosive nature.

9. Biodiesel Production:

In biodiesel production, caustic soda is used in the transesterification process to convert vegetable oils or animal fats into biodiesel and glycerol.

10. Textile Dyeing:

Caustic soda is used in the dyeing process to prepare fabrics for dye absorption. It helps to increase the affinity of fabrics for certain types of dyes.



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